Two-Point Composition-Temperature Control of Binary Distillation Columns

Although the two-input-two-output (2I-2O) dual composition (DC) and two-point temperature (TPT) distillation control problems have been studied extensively, the development of two-input-four-output (2I-4O) composition-temperature (CT) control schemes, driven by two composition and two temperature measurements, lags far behind. The difficulty of the 2I-4O CT control problem is due to the lack of systematic means to screen the large number of combined structural-algorithmic design degrees of freedom. With contradictory results, the problem has been recently addressed with linear and nonlinear approaches. Based on a constructive control framework, in this work, a rather simple solution to the combined 2I-4O CT control problem is obtained. The resulting scheme consists of linear PI components and static interaction compensators, has a systematic construction procedure with reduced model dependency, and has easy-to-apply tuning guidelines. The proposed approach is applied to three representative examples through simulations, yielding behaviors that improve those of previous linear and nonlinear cascade control schemes.